Indeed. Which is why I think Amazon might take a more Alexa-like approach to HD Music, i.e. be open to integrating with third-party hardware because it realises that every user of non-Amazon hardware that connects to the service is still paying a monthly sub to Amazon that helps build, as you say, a regular predictable income stream. Roon potentially brings a whole host of very high-end hardware to the Amazon ecosystem in one fell swoop if it were to be integrated. Despite the vast size of Amazon’s user base vs Roon, Roon is very concentrated on the very high end and Amazon just might see value in early strong momentum and find the thought of bringing all those DACs and high-end streamers and active speakers into their ecosystem in the first few months attractive.
All we can do is sit and wait and, as @bitonio very rightly pointed out, all file requests for Roon integration directly with Amazon via its feedback mechanism - it certainly can’t do any harm and might just help.